The mass walk out was set to happen ahead of Labour’s ruling national executive committee (NEC) is set to confirm Ms Formby’s appointment today.

Concerns have been raised that Ms Formby was involved in giving work to Vicki Kirby who had previously been suspended by the party for antisemitism when she was a senior figure in the Unite union.

Ms Formby’s appointment is a victory for her ex-lover Unite boss Len McCluskey and is seen as the final step in the far Left’s takeover of Labour.

She replaces moderate Iain McNicol who was understood to have been forced out by allies of leader Jeremy Corbyn.

According to reports John Stolliday, Labour’s head of governance and legal, is one of at least half a dozen to walk out en mass.

Quitting after working for the party for 14 years, Mr Stolliday emailed: “I have been honoured to work under four party leaders – including two Prime Ministers – as well as Ed and Jeremy in opposition, and also Harriet as interim leader who has done so much for our Party and movement across the years.

“I want to thank you all for the support, kindness, patience and friendship you have shown to me over so many years and leave knowing that the Labour party is well set to advance at the next general election, whenever that happens.”

London regional director Neil Fleming and Parliamentary Labour Party secretary Dan Simpson are leaving while policy research director Simon Jackson is quitting after 18 years.